Leakage efficient anti-glitch filter

ABSTRACT

A leakage efficient anti-glitch filter. In accordance with a first embodiment of the present invention, a leakage efficient anti-glitch filter with variable delay stages comprises a plurality of variable delay stages and a coincidence detector element for detecting coincidence of an input signal to the delay element and an output of the delay element. The plurality of variable delay stages may comprise stacked inverter circuits or stacked NAND circuits.

RELATED APPLICATIONS

This is a Continuation Application of, and claims benefit to, co-pendingU.S. patent application Ser. No. 11/021,197, filed Dec. 23, 2004, toMasleid, which is hereby incorporated herein by reference in itsentirety, which is a Continuation-in-Part of co-pending, commonly ownedU.S. patent application Ser. No. 10/864,271, filed Jun. 8, 2004,entitled “Stacked Inverter Delay Chain” to Masleid and Burr, which ishereby incorporated herein by reference in its entirety.

This Application is related to the following, commonly assigned UnitedStates Patents or Applications, which are hereby incorporated herein byreference in their entirety:

U.S. patent application Ser. No. 11/021,222, filed Dec. 23, 2004,entitled “A Configurable Tapered Delay Chain with Multiple Sizes ofDelay Elements” by Masleid;

U.S. patent application Ser. No. 11/021,221, filed Dec. 23, 2004,entitled “A Configurable Delay Chain with Switching Control for TailDelay Elements” by Masleid;

U.S. patent application Ser. No. 11/021,632, filed Dec. 23, 2004,entitled “Power Efficient Multiplexer” to Masleid;

U.S. patent application Ser. No. 11/020,746, filed Dec. 23, 2004, nowU.S. Pat. No. 7,310,008, entitled “A Configurable Delay Chain withStacked Inverter Delay Elements” by Masleid; and

U.S. patent application Ser. No. 11/021,633, filed Dec. 23, 2004, nowU.S. Pat. No. 7,330,054, entitled “Leakage Efficient Anti-glitch Filter”by Masleid.

FIELD OF THE INVENTION

Embodiments in accordance with the present invention relate to leakageefficient anti-glitch filters with variable delay stages.

BACKGROUND

It is sometimes advantageous to delay propagation of a signal through anintegrated circuit. A common approach to create such signal delays is toinsert a delay circuit, or delay “line,” into a signal path. One wellknown class of delay circuits is a variable delay circuit. For example,a variable delay circuit can function by selectably varying a number ofdelay elements to produce different amounts of delay to a signalpropagating through such elements. However, in general, variable delaylines can generate “glitches” or deleterious spurious signals. Forexample, changing a delay duration while a transition is propagatingthrough the delay line can sometimes cause the transition to arrivetwice at the output, producing a glitch. Further, it is generallydesirable for delay circuit designs to be efficient in terms ofintegrated circuit die area, active power consumption and static power(leakage current) consumption.

SUMMARY OF THE INVENTION

A leakage efficient anti-glitch filter with variable delay stages isdisclosed. In accordance with a first embodiment of the presentinvention, a leakage efficient anti-glitch filter with variable delaystages comprises a plurality of variable delay stages and a coincidencedetector element for detecting coincidence of an input signal to thedelay element and an output of the delay element. The plurality ofvariable delay stages may comprise stacked inverter circuits or stackedNAND circuits.

In accordance with another embodiment of the present invention, a methodof delaying an electronic signal is disclosed. An electronic signal isaccessed. A delayed version of the electronic signal is produced througha variable number of delay stages. The electronic signal and the delayedversion of the electronic signal are combined to produce a glitch-freedelayed electronic signal. The glitch-free delayed electronic signaltransitions in response to a coincidence of the electronic signal andthe delayed version of the electronic signal.

In accordance with still another embodiment of the present invention, anelectronic circuit is disclosed. The electronic circuit comprises adelay line comprising a plurality of stacked inverters coupled inseries. Each of the plurality of stacked inverters comprises at leasttwo devices of a first type coupled in series, coupled in series to atleast two devices of an opposite type coupled in series. The electroniccircuit further comprises a plurality of multiplexers corresponding tothe plurality of delay stages for selecting between a signal present ata desired delay stage and a signal propagating from beyond a delay stagecorresponding to a multiplexer. The electronic circuit further comprisesa coincidence detector circuit. The coincidence detector circuitcomprises first and second devices of a first type coupled in series,coupled in series to third and fourth devices of a second type coupledin series. An input to the delay line is coupled to gates of the firstand fourth devices and an output of the delay line is coupled to gatesof the second and third devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic of a novel leakage efficient anti-glitchfilter, in accordance with embodiments of the present invention.

FIG. 2 is a timing diagram illustrating a function of a leakageefficient anti-glitch filter, in accordance with embodiments of thepresent invention.

FIG. 3 illustrates a flow chart describing a method of filteringglitches from an electronic signal, in accordance with embodiments ofthe present invention.

FIG. 4 illustrates a leakage efficient anti-glitch filter with variabledelay stages, in accordance with embodiments of the present invention.

FIG. 5 illustrates a flow chart describing a method of delaying anelectronic signal, in accordance with embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the present invention, leakageefficient anti-glitch filter with variable delay stages, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be recognizedby one skilled in the art that the present invention may be practicedwithout these specific details or with equivalents thereof. In otherinstances, well-known methods, procedures, components, and circuits havenot been described in detail as not to unnecessarily obscure aspects ofthe present invention.

Leakage Efficient Anti-Glitch Filter

Embodiments in accordance with the present invention are described inthe context of design and operation of integrated semiconductors. Moreparticularly, embodiments of the present invention relate to leakageefficient anti-glitch filters. It is appreciated, however, that elementsof the present invention may be utilized in other areas of semiconductordesign and operation.

The following description of embodiments in accordance with the presentinvention is directed toward pFETs (or p-type metal oxide semiconductorfield effect transistors (MOSFETS)) formed in surface N-wells and/ornFETs (or n-type MOSFETS) formed in surface P-wells when a p-typesubstrate and an N-well process are utilized. It is to be appreciated,however, that embodiments in accordance with the present invention areequally applicable to nFETs (or n-type MOSFETS) formed in surfaceP-wells and/or pFETs (or p-type MOSFETS) formed in surface N-wells whenan n-type substrate and a P-well process are utilized. Consequently,embodiments in accordance with the present invention are well suited tosemiconductors formed in both p-type and n-type materials, and suchembodiments are considered within the scope of the present invention.

FIG. 1 illustrates a schematic of a novel leakage efficient anti-glitchfilter 100, in accordance with embodiments of the present invention.Leakage efficient anti-glitch filter 100 comprises an optional inputbuffer 110, a leakage efficient delay line 120 and a coincidencedetector element 130.

Optional input buffer 110 can provide transition speed isolation. Forexample, without optional input buffer 110, leakage efficient delay line120 presents six loads at its input. Such loading may represent anundesirable loading condition to the source of a signal. In accordancewith embodiments of the present invention, input buffer 110 is wellsuited to a variety of buffering structures, including, for example,conventional or stacked inverters and non-inverting buffers.

It is to be appreciated that static power consumption in modernsemiconductor processes, e.g., processes with a minimum feature size ofabout 0.13 microns and smaller, is no longer a negligible component oftotal power consumption. For such processes, static power may beone-half of total power consumption. Further, static power, as apercentage of total power, is tending to increase with successivegenerations of semiconductor process.

Embodiments in accordance with the present invention offer significantadvantages in reducing leakage current, or static power consumption, incomparison with the conventional art. In general, an inverter stage,whether conventional or stacked, forms a leakage path, e.g., a series“string” of devices coupled from operating voltage (Vdd) to ground. Ascurrent leaks out of such leakage paths, static power is consumed by theinverter stage. As described more completely in U.S. patent applicationSer. No. 10/864,271, entitled “Stacked Inverter Delay Chain” to Masleidand Burr, incorporated herein by reference in its entirety, a delaychain comprising stacked inverters can require fewer stages than a delaychain comprising conventional inverters to produce a comparable delay.For example, each stage of stacked inverters will generally producegreater delay than a conventional, non-stacked inverter. Fewer stagesresult in fewer leakage paths, resulting in advantageously less leakagecurrent, resulting in less static power consumption.

Further, such leakage paths within a stacked inverter suffer lessleakage than a conventional inverter, yielding additional beneficialleakage reductions. In a conventional inverter, exactly one transistoris on while the other transistor is off. As an unfortunate consequence,approximately the full bias voltage is applied to the off transistor,resulting in a maximum possible leakage for the off transistor.

In contrast, in a stacked inverter multiple transistors are either on oroff in series. For example, in the embodiment of FIG. 1, for a “high”state, two transistors are on, while two transistors are off.Consequently, each “off” transistor has significantly less than fullbias voltage applied. It is appreciated that leakage current generallydecreases exponentially as voltage decreases. For example, a factor oftwo reduction in off bias voltage produces about a factor of eightreduction in leakage current per leakage path.

It is to be further appreciated that such leakage induces non zerovoltages at intermediate nodes between the off transistors Such voltagesinduce body effects in the transistors. Such body effects increase thethreshold voltage of the affected transistors. An increased thresholdvoltage generally produces beneficial decreases in leakage current.

Consequently, in addition to a decrease in a number of leakage paths, inaccordance with embodiments of the present invention, the leakagecurrent of each path is very beneficially reduced due to an induced bodyeffect and a highly non-linear relationship between bias voltage andleakage current. Thus, leakage efficient delay line 120 significantlyreduces static power consumption, in comparison to a delay linecomprising conventional inverters.

Leakage efficient delay line 120 comprises a plurality of stackedinverters. The output of a first stacked inverter is generally coupledto the input of a subsequent stacked inverter. It is to be appreciatedthat more or fewer stacked inverters can be included in leakageefficient delay line 120 in order to achieve differing signal delayvalues, in accordance with embodiments of the present invention.

For example, physical differences between electrons and holes, andbetween n-type and p-type dopants, as well as constructive differencesin device geometry and dopant placement, result in differences inefficiency between n-type devices and p-type devices. Because electronmobility is higher than hole mobility, n-type devices are more efficientthan p-type devices. However, the degree of difference depends onconstructive differences that can vary with process. Such physical andconstructive differences also produce other behavior differences, suchas a difference in sensitivity to body effects. Consequently, differentlevels of benefit, e.g., in leakage reduction, are to be expectedbetween stacks of n-type devices and stacks of p-type devices. To allowfor such effects, in accordance with embodiments of the presentinvention, it is possible to stack different numbers of transistors oneither or both legs of a stacked inverter. Such variations allowincreases in load and/or decreases in drive capability, enabling a widevariety of delay values, as well as enabling differing body effects.

In contrast to a conventional inverter, the stacked inverters of leakageefficient delay line 120 comprise more than a single p-type devicecoupled to a single n-type device. Rather, the stacked inverters ofleakage efficient delay line 120 comprise multiple p-type devices andmultiple n-type devices. In the embodiment of FIG. 1, the inverters areshown as comprising two p-type devices and two n-type devices. It isappreciated that embodiments of the present invention are well suited toa variety of stacking combinations of p-type and n-type devices, as wellas to other delay elements, for example leakage efficient, e.g.,stacked, NAND gates.

As will be discussed further below, the signal delay produced by leakageefficient delay line 120 is related to the duration of spurious signals,or glitches, that are to be filtered by leakage efficient anti-glitchfilter 100.

Still referring to FIG. 1, coincidence detector element 130 functions tocombine signal A 111, the input of leakage efficient delay line 120,with signal B 121, the output of leakage efficient delay line 120.Coincidence detector element 130 will only propagate a signal whensignals A 111 and B 121 coincide.

In the embodiment of FIG. 1, coincidence detector element 130 comprisesa “Mueller-C” element. It is appreciated that embodiments of the presentinvention are well suited to other types of coincidence detectors. AMueller-C element is a well known special type of NAND gatecharacterized by propagating a state change only when both of its inputsagree. For example, a true NAND (or AND) gate can transition from trueto false when only one of its inputs changes from true to false. Incontrast, coincidence detector element 130 does not transition until allinputs agree. e.g., both inputs change from true to false.

For example, only when both signal A 111 and signal B 121 are low willthe pFET devices of coincidence detector element 130 turn on and pulloutput signal C 131 to a high condition. Similarly, only when bothsignal A 111 and signal B 121 are high will the nFET devices ofcoincidence detector element 130 turn on and pull output C 131 to a lowcondition.

Conventionally, coincidence detector elements, e.g., a Mueller-Celement, are generally utilized to compare or combine disparate signals.For example, a conventional use of such elements is to determinecompletion of a logic function.

In contrast, in accordance with embodiments of the present invention,coincidence detector element 130 receives as input the input to leakageefficient delay line 120 and the output of leakage efficient delay line120. Thus, coincidence detector element 130 receives a signal and adelayed version of the same signal.

Leakage efficient anti-glitch filter 100 suppresses any glitch orspurious signal characterized as having a duration of less than thedelay characteristic of leakage efficient delay line 120.

It is generally desirable for a delay circuit, e.g., leakage efficientdelay line 120, to track speed changes of other circuitry of anintegrated circuit. It is appreciated that a variety of factors, e.g.,operating voltage, operating temperature and/or manufacturing processvariations, can affect the speed of operation of an integrated circuit.For example, if other circuits of an integrated circuit operate faster,generally less absolute delay is required from a delay circuit for theoverall circuit to function. By way of further example, if othercircuits of an integrated circuit operate more slowly, it may beadvantageous for leakage efficient delay line 120 to operate moreslowly, e.g., with greater absolute delay, in order to remove longerglitches generated by such slower operating other circuitry. Becauseembodiments in accordance with the present invention comprise stackeddevices, they are similar to many logic circuits that also comprisestacked devices, e.g., NAND and/or NOR logic gates. Consequently,embodiments in accordance with the present invention match or trackchanges in operating speed of complex logic more accurately than delaychains comprising very simple inverters.

Embodiments in accordance with the present invention are thus shown tooffer significant and highly beneficial improvements in tracking timingchanges of other circuits and in static power (leakage current)consumption in comparison to the conventional art.

FIG. 2 is a timing diagram 200 illustrating a function of leakageefficient anti-glitch filter 100, in accordance with embodiments of thepresent invention. Timing diagram 200 shows a relationship amongexemplary signals associated with leakage efficient anti-glitch filter100.

Signal A 210 is an input waveform to leakage efficient anti-glitchfilter 100. Signal A 210 is one possible signal corresponding to signalA 111 of FIG. 1. Signal A 210 comprises a glitch 220 and a desiredtransition 230.

Signal B 240 is a delayed version of signal A 210, corresponding to theoutput B 121 of leakage efficient delay line 120 (FIG. 1). Signal B 240is a reproduction of signal A 210, delayed by a duration 245. It is tobe appreciated that duration 245 corresponds to the delay of leakageefficient delay line 120 of FIG. 1. Signal B 240 comprises a glitch 250,corresponding to glitch 220, and a desired transition 260, correspondingto desired transition 230. It is to be appreciated that glitch 250 anddesired transition 260 are delayed by duration 245 in relation to theircorresponding elements of signal A 210. It is to be further appreciatedthat glitch 220 is of a time duration that is less than delay duration245.

Signal C 270 is an output of leakage efficient delay line 120 as viewedat output C 131 (FIG. 1) when excited by signal A 210. It is appreciatedthat desired transition 280 of signal C 270 does not occur until bothsignal A 210 and signal B 240 agree. For example, at a time beforedesired transition 280, signal B 240 is low. Consequently, changes insignal A 210, e.g., glitch 220 and/or desired transition 230, do notaffect signal C 270.

At the time of desired transition 280, signal A 210 is high, and signalB 240 transitions to high. Consequently, signal C 270 transitions tolow, producing desired transition 280. As signal A 210 is high for theremaining duration of timing diagram 200, changes in signal B 240, e.g.,glitch 250 and/or desired transition 260, do not affect signal C 270.

Thus, in accordance with embodiments of the present invention, aspurious signal, e.g., glitch 220, present on an input to leakageefficient anti-glitch filter 100 (FIG. 1) is removed, and is not presenton the output of leakage efficient anti-glitch filter 100.

It is to be appreciated that signal C 270 is inverted relative to signalA 210. Referring once again to FIG. 1, the output of leakage efficientanti-glitch filter 100, e.g., signal C 131, can be inverted by aninverting circuit (not shown) to obtain a positive phase relationship toa signal input to leakage efficient anti-glitch filter 100.Alternatively, an inverting optional input buffer 110 can “pre-invert” asignal input to leakage efficient anti-glitch filter 100 in order toobtain a positive phase relationship between an input signal and anoutput signal.

FIG. 3 illustrates a flow chart describing a method 300 of filteringglitches from an electronic signal, in accordance with embodiments ofthe present invention. In 310, an electronic signal is accessed. Forexample, referring once again to FIG. 1, signal A 111 is accessed byleakage efficient anti-glitch filter 100.

In 320, a delayed version of the electronic signal is produced. Forexample, signal B 121 is a delayed version of signal A 111 in FIG. 1. In330, the electronic signal and the delayed version of the electronicsignal are combined to produce a glitch-free electronic signal. Theglitch-free electronic signal transitions in response to a coincidenceof the electronic signal and the delayed version of the electronicsignal.

Leakage Efficient Anti-Glitch Filter with Variable Delay Stages

FIG. 4 illustrates a leakage efficient anti-glitch filter with variabledelay stages 400, in accordance with embodiments of the presentinvention. It is to be appreciated that the embodiment of FIG. 4illustrates a variable delay chain with uniform delay stages.Embodiments in accordance with the present invention are well suited toa wide variety of delay chains, including non-uniform, e.g., tapered,delay chains and/or delay chains with variable elements per tap. It isto be further appreciated that embodiments in accordance with thepresent invention are well suited to greater numbers of selectable delaystages than illustrated.

Leakage efficient anti-glitch filter with variable delay stages 400comprises a plurality of selectable delay stages, e.g., selectable delaystages 440 and 450. It is appreciated that selectable delay stages 440and 450 form a variable delay line. Each selectable delay stagecomprises a delay element, e.g., delay element 441 of selectable delaystage 440.

In the embodiment of FIG. 4, delay element 441 comprises a stacked2-input NAND gate. It is to be appreciated that other types of delayelements, e.g., a stacked inverter, are well suited to embodiments inaccordance with the present invention. It is to be appreciated that adelay chain comprising stacked NAND gates can require fewer stages thana delay chain comprising conventional NAND gates to produce a comparabledelay. For example, each stage of stacked NAND gates will generallyproduce greater delay than a conventional, non-stacked NAND gate. Fewerstages result in fewer leakage paths, resulting in advantageously lessleakage current, resulting in less static power consumption.

It is appreciated that leakage current generally decreases exponentiallyas voltage decreases. For example, a factor of two reduction in off biasvoltage produces about a factor of eight reduction in leakage currentper leakage path. Consequently, as the operating voltage is distributedacross more devices in a stacked NAND gate, as opposed to a conventionalNAND gate, each “off” transistor has significantly less than full biasvoltage applied, and that this effect further reduces leakage current.

It is to be further appreciated that current leakage induces non zerovoltages at intermediate nodes between the off transistors. Suchvoltages induce body effects in the transistors. Such body effectsincrease the threshold voltage of the affected transistors. An increasedthreshold voltage generally produces beneficial decreases in leakagecurrent.

Consequently, in addition to a decrease in a number of leakage paths, inaccordance with embodiments of the present invention, the leakagecurrent of each path is very beneficially reduced due to an induced bodyeffect and a highly non-linear relationship between bias voltage andleakage current. Thus, delay element 441 significantly reduces staticpower consumption, in comparison to a delay element comprisingconventional NAND gates or conventional inverters.

The 2-input NAND gate of the illustrated embodiment advantageouslytracks timing changes, e.g., due to process variation, operating voltageand/or operation temperature, of other similarly constructed elements.For example, co-pending, commonly owned U.S. patent application Ser. No.11/021,221, filed Dec. 23, 2004, entitled “A Configurable Delay Chainwith Switching Control for Tail Delay Elements” to Masleid, incorporatedherein in its entirety by reference, discloses a variable delay chaincomprising a plurality of 2-input NAND gates as delay and controlelements. Delay element 441 can beneficially track timing changes ofsuch exemplary variable delay chain elements.

Leakage efficient anti-glitch filter with variable delay stages 400further comprises a multiplexer element, e.g., multiplexer element 442of selectable delay stage 440. In general, the multiplexer element of aselectable delay stage selects between a signal present at the output ofthe associated delay stage delay element and a signal propagated fromsubsequent delay stages.

Multiplexer element 442 selects between a signal propagated fromsubsequent delay stages, e.g., signal 451 propagated from themultiplexer element of selectable delay stage 450, and signal 452associated with its own selectable delay stage 440. A bit value in latch455 determines which signal, 451 or 452, is selected by multiplexerelement 442. A more detailed description of the operation of multiplexerelement 442 is presented in co-pending, commonly owned U.S. patentapplication Ser. No. 11/021,632, filed Dec. 23, 2004, entitled “PowerEfficient Multiplexer” to Masleid, incorporated herein by reference inits entirety.

For example, if multiplexer element 442 selects the output of anothermultiplexer element, e.g., signal 451, more delay elements have delayedan original signal, and the total delay is longer. In contrast, ifmultiplexer element 442 selects the output of its own delay element,e.g., signal 452, fewer delay elements have delayed an original signal,and the total delay is lessened.

In general, variable delay lines, for example, the variable delay lineformed by selectable delay stages 440 and 450, can generate “glitches”or deleterious spurious signals. For example, changing a multiplexercontrol signal while a transition is propagating through the delay linecan sometimes cause the transition to arrive twice at the output,producing a glitch.

Coincidence detector element 430 generally corresponds to coincidencedetector element 130 of FIG. 1. Referring once again to FIG. 4, it is tobe appreciated that the variable delay line formed by selectable delaystages 440 and 450 produces a delayed version of input signal A 411.That delayed version of input signal A 411 is signal B 421. As describedpreviously, coincidence detector element 430 does not change state untilinput signal A 411 and signal B 421 coincide, or are at the same level.

Advantageously, any glitch produced by incrementing the delay of aseparate variable delay line formed by selectable delay stages similarto stages 440 and 450 will generally be of shorter duration than thedelay produced by delay stages 440 and 450, when the appropriate latchesare set to one. As coincidence detector element 430 serves to filterglitches of duration less than the delay between its inputs, e.g., thedelay between signal A 411 and signal B 421, coincidence detectorelement 430 will generally filter any glitch shorter than the totaldelay of delay stages 440 and 450.

For example, if a separate variable delay line is incremented two stagesat a time, then the glitch filter should contain a delay of four stagesto allow for a 2:1 process mismatch.

It is to be appreciated that this general timing relationship will holdfor a plurality of delay stages, in accordance with embodiments of thepresent invention.

Optional input buffer 410 can provide transition speed isolation. Forexample, without optional input buffer 410, leakage efficientanti-glitch filter with variable delay stages 400 presents six loads atits input. Such loading may represent an undesirable loading conditionto the source of a signal. In accordance with embodiments of the presentinvention, input buffer 410 is well suited to a variety of bufferingstructures, including, for example, conventional or stacked invertersand non-inverting buffers.

A timing diagram for signals A 441, B 421 and C 431 of FIG. 4corresponds to timing diagram 200 of FIG. 2. Signal B 421 is a delayedversion of signal A 441. It is appreciated that delay is a primaryfunction of selectable delay stages 440 and 450. It is to be furtherappreciated that, in general, a delay produced by selectable delaystages 440 and/or 450 will comprise a different duration than a delayproduced by leakage efficient delay line 120 of FIG. 1.

As described previously, coincidence detector element 430 does notchange state until input signal A 411 and signal B 421, a delayedversion of signal A 411, coincide, or are at the same level. It isappreciated that a desired transition of signal C 431, corresponding toa desired transition of signal A 411, does not occur until both signal A411 and signal B 421 agree.

Thus, in accordance with embodiments of the present invention, aspurious signal, e.g., a glitch applied to the variable delay lineformed by selectable delay stages 440 and/or 450 is removed and is notpresent on the output signal C 431 of leakage efficient anti-glitchfilter with variable delay stages 400 if the glitch present on the inputof selectable delay stage 440 is of less duration than the delayproduced by selectable delay stages 440 and/or 450.

It is to be appreciated that signal C 431 is inverted relative to signalA 411. The output of leakage efficient anti-glitch filter with variabledelay stages, e.g., signal C 431, can be inverted by an invertingcircuit (not shown) to obtain a positive phase relationship to a signalinput to leakage efficient anti-glitch filter 100. Alternatively, aninverting optional input buffer 410 can “pre-invert” a signal input toleakage efficient anti-glitch filter with variable delay stages 400 inorder to obtain a positive phase relationship between an input signaland an output signal.

FIG. 5 illustrates a flow chart describing a method 500 of delaying anelectronic signal, in accordance with embodiments of the presentinvention. In 510, an electronic signal is accessed. For example,referring once again to FIG. 4, signal A 411 is accessed by selectabledelay stage 440.

In 520, a delayed version of the electronic signal is produced through avariable number of delay stages. For example, signal B 421 is a delayedversion of signal A 411 in FIG. 4. Signal B 421 can be delayed through avariable number of delay stages, e.g., selectable delay stages 440and/or 450.

In 530, the electronic signal and the delayed version of the electronicsignal are combined to produce a glitch-free delayed electronic signal.The glitch-free delayed electronic signal transitions in response to acoincidence of the electronic signal and the delayed version of theelectronic signal.

Embodiments in accordance with the present invention thus provide aleakage efficient anti-glitch filter with variable delay stagescomprising desirable static power (leakage current) consumption incomparison to the conventional art.

Embodiments in accordance with the present invention, leakage efficientanti-glitch filter, are thus described. While the present invention hasbeen described in particular embodiments, it should be appreciated thatthe present invention should not be construed as limited by suchembodiments, but rather construed according to the below claims.

1. An anti-glitch filter circuit comprising: a delay element comprising a stacked gate configured to produce a variable delay; and a coincidence detector element configured to detect coincidence of an input signal to the delay element and an output signal of the delay element, wherein the coincidence detector element includes a glitch-filtered output signal output, wherein said variable delay is configured for digital control.
 2. The anti-glitch filter circuit of claim 1, wherein the glitch-filtered output signal output is configured such that spurious signals having a duration of less than a delay of the delay element are substantially eliminated.
 3. The anti-glitch filter circuit of claim 2, wherein the coincidence detector element comprises a Mueller-C element.
 4. The anti-glitch filter circuit of claim 2, wherein the stacked gate comprises a NAND gate.
 5. The anti-glitch filter circuit of claim 1 wherein the stacked gate comprises a stacked NAND-gate circuit.
 6. The anti-glitch filter circuit of claim 5 wherein the stacked NAND-gate circuit comprises at least two p-type devices and at least two n-type devices.
 7. The anti-glitch filter circuit of claim 6 wherein the stacked NAND-gate circuit is configured to have a greater switching time duration than an inversion performed by an inverter comprising only four active devices.
 8. The anti-glitch filter circuit of claim 6 wherein the stacked NAND-gate circuit is configured to have less leakage current than an inverter comprising only four active devices.
 9. The anti-glitch filter circuit of claim 6, wherein the stacked NAND-gate circuit comprises: a first plurality of devices of a first type coupled in series; and a second plurality of devices of a second type coupled in series, wherein the second type is opposite to the first type; wherein the first and the second pluralities of devices are coupled in series and include at least five active devices.
 10. A method of delaying an electronic signal, the method comprising: accessing an electronic signal; producing a delayed version of the electronic signal through a digitally controlled variable delay stage; and combining the electronic signal and the delayed version of the electronic signal to produce a substantially glitch-free delayed electronic signal, wherein the glitch-free delayed electronic signal transitions in response to a coincidence of the electronic signal and the delayed version of the electronic signal.
 11. The method of claim 10, wherein said combining comprises filtering glitches characterized as having a duration of less than a delay of said delayed version of said electronic signal.
 12. The method of claim 10, wherein said combining is performed using a Mueller-C element.
 13. The method of claim 10, wherein said producing is performed using a plurality of inverters.
 14. The method of claim 13, wherein the plurality of inverters comprise a stacked inverter circuit.
 15. The method of claim 14, wherein the stacked inverter circuit comprises at least two p-type devices coupled in series with at least two n-type devices.
 16. The method of claim 15, wherein the stacked inverter circuit has a greater switching time duration than an inversion performed by an inverter comprising only two active devices.
 17. The method of claim 15, wherein the stacked inverter circuit has less leakage current than an inverter comprising only two active devices.
 18. The method of claim 15, wherein the stacked inverter circuit comprises: a first plurality of devices of a first type coupled in series; and a second plurality of devices of a second type coupled in series, wherein the second type is opposite to the first type; wherein the first and the second pluralities of devices are coupled in series and comprise at least five active devices.
 19. An electronic circuit comprising: a plurality of delay stages including a plurality of stacked inverters coupled in series, wherein each of the plurality of stacked inverters comprise: at least two devices of a first type coupled in series, wherein the at least two devices of a first type are further coupled in series to at least two devices of a second type coupled in series; wherein the second type is opposite to the first type; a plurality of multiplexers corresponding to the plurality of delay stages and configured to select between a signal present at a desired delay stage and a signal propagating from beyond a delay stage corresponding to a multiplexer; and a coincidence detector circuit including first and second devices of a first type coupled in series, wherein the first and second devices of a first type are further coupled in series to third and fourth devices of a second type coupled in series.
 20. The electronic circuit of claim 19, wherein gates of each device of the plurality of stacked inverters are coupled together. 